Oil pressure relief, oil cooler, and accusump interaction Options

[Seabird]

Good morning everyone. I am in the process of upgrading my oil system. This is on my dedicated track 914. The upgrades include remote oil cooler, accusump, and CB Maxi oil pump.

In my research for installing the accusump it seems like there are two places that are recommended, in the cooler return line with a check valve and direct to the block. I did not want to use the sandwich plate adapter so I opted for the block option. Simpler with less seals to fail.

As I looked into the workings of the type IV oil system I found a potential problem with both these locations; the oil relief valve on the front of the engine. VW used this valve to bypass the cooler when the oil is thick. But this also means the cooler is bypassed when the oil pressure is high. Does the use of an oil accumulator negate the oil cooler system by maintaining oil pressure?

While on the straights the pump could potentially make 50-60 psi of oil pressure. (the 30mm pump that was in the engine produces those pressures much of a 20 min session) At those oil pressures the cooler will be bypassed based on what I know of the relief valve (bypassing cooler at 60psi, partially open at 35 psi, and sealed at 12psi). The accusump will also build up to that pressure. When I go to brakes and the revs drop the accusump will start pushing back and keep the pressure up till the differential is corrected. If I am back on to the next straight in that time then the pump starts building the pressure again.

Options:

1. Am I making a mountain out of a mole hill? Leave it alone.

2. Plug that relief valve so it stays closed and let the oil cooler thermostat bypass the oil when its cold. This is a pre 76 case so there is the secondary relief valve by cylinder 1. Might be able just to invert the piston so the bypass grove is below the bypass passages.

3. There is also the high pressure pistons sold by pelican parts and others. Does this just shift the bypass window to a higher pressure range?

I would love to hear people's thoughts on this.

Miguel

[Seabird]

Track Test Report:

Was back up at Sebring this weekend with my 914 facing the grueling heat of central Florida in June. Surface temp of the track was upwards of 127 deg F when I measured it at mid day after one of my sessions. It was hot.

(IMG:http://www.914world.com/bbs2/uploads_offsite/dl.dropboxusercontent.com-16683-1403626412.1.jpg)

The cooler and pressure relief kits did their jobs well.

First thing I need to mention is the error in my VDO gauge. At the end of a 25 minute session the gauge was indicating 260 degree oil temp. As soon as I arrived in my pit I measure temperatures in several locations, oil cooler fins, tuna can, crank case sump (aluminum), and oil filter. Not a single one of these approached 260*. The closest reading was found on the cooler and the oil filter and they read 220*. That's a 40 degree error, on a new gauge!!

Temps were as follows:
oil cooler 215-220 depending where it was measured
Tuna can 180
Crank case 190
Oil filter 220

The oil pressure issues I was having were solved and were probably due to installer error in setting the acussump pre-charge.

While making changes and tweaks to the oiling system I closed off the top portion of the oil cooler box and added a scoop to the bottom to try and avoid picking up exhaust wash. Additionally I added a fresh air duct from the fan in the front valance to the cooler box.

(IMG:http://www.914world.com/bbs2/uploads_offsite/dl.dropboxusercontent.com-16683-1403626415.2.jpg)

The difference between the current set up and how Chris supplies the kit on track really only came down to how quickly the oil came up to its peak temp of 220. Without the extras the temp would come up to 220 within 3-4 laps and with the extras it would take 5-6 laps. If 220 is the ideal operating temp, which some folks promote, then the extra work was in vain.

I like that I can get a little extra cooling while idling back to my pit stall.

Throughout the session I was checking my oil pressure. Better than 50 psi was observed from the start of the session till the end. Only at idle rpms while heading back to the pits did the pressures drop. With the block off sleeve in place I am certain that all the oil running through the galleys first went through the cooler.

I am very happy with the results. If I end up with a bigger motor or a 6 I may have to swap to a front mount cooler. But if it could handle a 25 min session at Sebring in June I think it can handle just about anything its going to see with me at the wheel.

I was only able to run a session an a half as I developed a fuel starvation problem on Saturday afternoon. So now there is a new problem to address but at the least I have an oiling system that is up too par. Thanks Chris!!

Miguel